Alzheimer's disease (AD) is an irreversible neurodegenerative disorder with complex multifactorial pathological cascades, including amyloid-β (Aβ) aggregation, tau hyperphosphorylation, sustained neuroinflammation, oxidative stress, cholinergic dysfunction and gut-brain axis imbalance. Current marketed anti-AD drugs merely relieve symptomatic cognitive impairment without halting or reversing disease progression, highlighting an urgent demand for novel multi-target therapeutic candidates. Marine ecosystems, covering 71% of the Earth's surface, generate structurally unique, low-toxicity secondary metabolites via adaptive metabolic pathways of marine algae, invertebrates and microorganisms, which represent promising lead compounds for developing marine anti-AD therapeutics with synergistic multitarget neuroprotective activities. This systematic review comprehensively summarizes the anti-AD bioactivities and underlying molecular mechanisms of seven major categories of marine natural products, including marine polysaccharides, terpenoids, macrolides, alkaloids, polyphenols and carotenoids, sterols/lipids, and aminosulfonates. We further perform an integrated ADMET druggability assessment of representative marine bioactive molecules to evaluate their blood-brain barrier penetration, oral absorption, physicochemical properties and toxicological risks, identifying homotaurine as the most balanced candidate with favorable central nervous system delivery and safety profiles. We also elaborate the core bottlenecks restricting clinical translation, including insufficient blood-brain barrier permeability and unsatisfactory in vivo pharmacokinetic behaviors of most marine-derived compounds. Finally, we outline future research directions, covering structural modification, nanocarrier delivery, gut-brain axis-targeted intervention and cross-disciplinary translational research. This work aims to provide a comprehensive theoretical reference for the discovery, optimization and clinical transformation of marine anti-Alzheimer drugs, and facilitate high-value exploitation of marine bioactive resources for neurodegenerative disease treatment.
